The poorest areas that suffer the highest crime rates will be struck hardest by the government's cuts to police budgets, senior police figures have told the Guardian, with estimates predicting that 45,000 officers and staff face losing their jobs.

Whitehall funding for police will be cut by 20% over the next four years, leaving the money to be made up by council taxpayers. Urban areas will be hit hardest because they rely more on government grants to fund their police forces than rural areas. Police are funded by a mix of money directly given by central government, and by money raised from local council tax payers, which is called the precept.

Bob Jones, chair of the finance committee of the West Midlands Police Authority, said: "It is looking pretty horrendous. We will get hit twice as hard in percentage terms as Surrey does."

The government cut will amount to 10% of revenues in Surrey, but 18% in the West Midlands.

In the government's emergency budget in June, the money each force receives from Whitehall was cut by the same percentage, which Jones said was unfair. "Surrey is a low crime area, and had the lowest reduction, while the West Midlands got twice the cut. We wonder if the Conservatives are favouring their own areas at the expense of others."

A senior police source with close knowledge of the national state of funding confirmed the effect of the cut, saying: "As it stands the cuts will hit urban areas more severely. The majority of crime is in the urban areas."

Jones, a former chair of the Association of Police Authorities, said his West Midlands force was now predicting government cuts would mean over four years it needs to get rid of 1,050 police officers, from a total of 8,600, and 1,200 civilian staff.

Greater Manchester police are looking at losing 2,500 officers and staff over the same period.

Jones said across England and Wales up to 21,000 police officers and 25,000 police staff face losing their jobs. Nationally, fresh calculations for police leaders after the chancellor's announcement support that estimate of up to around 45,000 job losses, according to a senior police source with close knowledge of the national state of funding.

Ministers have been annoyed by predictions of job losses, accusing some in the police of scaremongering.

Jones said: "Police officers will have to rely on less support and will have to do more of their own administration. There is every prospect they will be off the streets, more of the time.

"I can't fail to see how the public will notice the difference. The chancellor must be the MP for cloud cuckoo land."

Government grants make up 80% of the budgets of the West Yorkshire and the Greater Manchester forces, 87.6% of the Northumbria force and 81.8% of all funding of policing in Merseyside.

Direct grants pay for three-quarters of policing by the Metropolitan police in London, but their funding arrangement is more complex because they are also paid for various national roles they perform.

The forces least reliant on government money are Surrey at 51.5%, Dorset at 55.6%, North Yorkshire at 56.2% and Gloucestershire at 57.7%.

The idea that council-tax rises will make up for the large cut in the government grant is unlikely, said Rob Garnham, the chair of the Association of Police Authorities: "If the public are facing cuts to their incomes through a pay freeze or having to make extra pension contributions, the last thing we should be doing is putting up council tax bills.

"We may have increases [to the precept] in line with inflation, but not to recoup the loss in government grant."